1. Field of the Invention
The present invention relates to an image processing device, an image capture device, an image processing method, and a program regarding a restoration process based on a point spread function.
2. Description of the Related Art
In an object image photographed through an image capture optical system, a so-called point spread phenomenon in which a point object has minute spread due to the influence of diffraction, aberration, or the like caused by the image capture optical system may be observed. A function representing a response to a point light source of an optical system is called a point spread function (PSF), and is known as a parameter responsible for resolution deterioration (blurring) of a photographic image.
The photographic image deteriorated in image quality due to the point spread phenomenon can be recovered in image quality through a point image restoration process based on the PSF. The point image restoration process is a process in which a deterioration characteristic (point image characteristic) caused by aberration or the like of a lens (optical system) is determined in advance, and point spread of the photographic image is cancelled through an image process using a restoration filter (recovery filter) according to the point image characteristic.
Various methods for the point image restoration process have been suggested, and for example, JP2011-059813A discloses an image processing device which performs image recovery for an image subjected to nonlinear correction using blind deconvolution. This image processing device includes a correction unit which performs correction for reducing nonlinear gradation correction for a photographic image subjected to nonlinear gradation correction, and an image recovery unit which performs image recovery by applying blind deconvolution to the photographic image with reduced gradation correction.
JP2013-020610A discloses an image processing device which reduces over-recovery of image data by an image recovery process. In this image processing device, an image recovery process is performed for color image data in an RGB format before a gamma process, the difference between amplification and attenuation of a pixel signal value by gamma correction is absorbed, and a limit value of a variation is calculated such that the maximum value of the variation of the pixel signal value becomes constant even after gamma correction. With this, the technical problems in that “a situation in which a deterioration state of image data actually obtained does not match a deterioration state of image data to be recovered by an image recovery filter occurs due to a saturated pixel”, and “image quality deterioration, such as undershoot or overshoot, occurs in an edge portion, and in particular, undershoot in a low luminance portion is amplified by a gamma process after an image recovery process” have been solved.
The point spread function of the optical system is used in a restoration technique of an image with an extended depth of focus, and JP2012-049759A discloses an image capture module which executes image restoration in a short period of time with excellent accuracy. In this photographing module, a restoration process is applied to a luminance signal after a synchronization process (demosaic process), whereby it is not necessary to separately provide parameters of the restoration process for RGB, and it is possible to accelerate the restoration process. Furthermore, adjacent pixels are put together in a predetermined unit and the common restoration process parameter is applied to this unit to perform a deconvolution process, whereby the accuracy of the restoration process is improved.